Focus Modulation Of Cylindrical Vector Beams Using 1D Photonic Crystal Lens With Negative Refraction

Cylindrical vector beams have special distribution properties of intensity and polarization. Researchers have proposed various methods to achieve and modulate the focusing of cylindrical vector beams, which has peculiar properties and wide application. However, the existing methods have their limitations.The most favorite method is to use micro structures because traditional lens can hardly achieve tighter focusing and flexibly modulate the focal field. Plasmonic lens can only focus radial polarization components of cylindrical vector beams and it has a high integration level. However, its application is limited by the polarization dependence. To widen the application area of cylindrical vector beams, micro structure lens should have the abilities of tight focusing without the polarization limitation and flexible modulating of the focal field.This paper takes advantage of negative refraction effect, which is effective for orthogonal polarized states, in the second band of 1D photonic crystals to focus all polarization components of cylindrical vector beams in sub-wavelength scale using cylindrical plano-concave structure. Furtherly, the transversal distribution of focal field is modulated by choosing different polarization components, and the longitudinal distribution of focal field is modulated by tailoring the exit surface of the lens. Based on this, we firstly propose 1D photonic crystal plano-cone lens structure to shape the focal field to be optical needle with long focal depth and optical tube. The transversal FWHM of optical needle equals the theoretical minimum one, which is 0.36λ. The longitudinal depth of focus can be modulated by changing the size of the lens. Based on the work of 1D photonic crystals, negative refraction effect is referred in the grating lens who is composed of only one kind of media. We get approximate results of focusing and modulating. Furtherly, negative refraction effect of only one kind of medium is used to modulate the cylindrical vector beams approximately.The work here provides a new vision in modulating cylindrical vector beams in sub-wavelength scale. The application range of negative material, especially 1D photonic crystals and grating lens, is extended to the modulation of cylindrical vector beams domain. The results in this paper can provide a theoretically reference for application area such as optical microscopy, optical micromachining, optical micro-manipulation, etc.